Compare ( diff ) content from two different remote servers

To get an idea of different files in directories just use ssh+rsync.

ssh -t user1@server1 rsync -nvrc --delete /path/to/dir/to/compare/ user2@server2:/path/to/dir/to/compare/

To check differences in a particular file use ssh+diff.

$ ssh -t user1@server1 'ssh -t user2@server2 cat /path/to/file | diff - /path/to/file'